The present invention is based on a handheld power fret saw.
From U.S. Pat. No. 5,027,518, a power fret saw of this type is known that in its design is comparable to a fret saw that is actuated manually; the typical U-shaped bracket has a handgrip protruding transversely at the bottom, with a motor housing, and the back side of the grip has a switch for controlling the energy supply to the motor.
Compared with manual fret saws, the known power tool has the advantage that the manual sawing motion is dispensed with.
The power fret saw according to the invention has the advantage that it is very light in weight, rests comfortably in the hand, and can be guided by the user in a way that is especially securely controllable.
The safety of manipulation is improved because the pistol-like base housing adjoining the handgrip is lengthened to the rear and in the operating position is braced on the user""s forearm.
Because the arms of the U-shaped bracket are multiple times, in particular twice, as long as the power fret saw blade, relatively large-area workpieces can be machined with the fret saw as far as their middle; that is, the maximum cutting depth into a boardlike workpiece measured from its edge inward is approximately 270 mm, which is relatively great.
Because the handgrip has the toggle switch of the on- and-off switch of the motor at the front, this toggle switch is especially easy to manipulate, in particular with the index finger.
Because the base housing receives the motor and drive means for moving the power fret saw blade back and forth, the blades are protected against dust and damage.
Because the upper arm of the bracket, on its free end, carries an end housing that receives clamping and guide means for releasable clamping of the power fret saw blade, these means are especially well protected against dust and damage.
Because the fret saw on the top of its base housing has a flat bearing face, structured with grooves and aligned with the other arm, for bracing a workpiece, the fret saw can be guided in an especially controlled, low-vibration way relative to the workpiece, so that saw cuts can be made virtually as cleanly as with a ruler or protractor.
Because the base housing of the fret saw can be coupled, and in particular locked, releasably to a sawing table that can be secured to a workbench, for instance, and the handgrip protrudes past the sawing table at the bottom in a way that is convenient to grasp, the fret saw with the sawing table secured on it can be used as an especially precisely positionable hand tool or can be used as a stationary tool, in the case of a sawing table flanged to a workbench.
Because the base housing of the power fret saw can be coupled without play to the sawing table via longitudinal guides, in particular discontinuous tongue-and-groove guides, the power fret saw can be inserted from above into the sawing table and combined with it in bayonet mount fashion without an auxiliary tool.
Because the power fret saw can be disconnected from the sawing table by pressing down on an overlockable pushbutton, the power fret saw can be released especially quickly and conveniently without an auxiliary tool.
Because the power fret saw has a workpiece holding-down device that can be displaced parallel to the power fret saw blade and at the same time acts as a finger guard, the workpiece to be machined is fixed in an especially well- controlled way relative to the power fret saw blade, so that precise sawing can be done.
Because the arms of the U-shaped bracket have flat free ends and each carry a leaf spring there, the leaf springs are connected positionally securely to the bracket, resting with their full surface thereon, and a parallel orientation of the two leaf springs to one another is possible for the sake of parallelogram-like guidance of the saw blade with a slight pendulum stroke.
Because the leaf springs on their free ends have a central fork slot, into each of which one fastening end of the power fret saw blade can be suspended releasably, clamping of the power fret saw blade by positive engagement, which is securer than the previously known clamping of power fret saw blades by nonpositive engagement by turning a wing nut, can be attained without tools.
Because the upper leaf springs are bent in a U and are secured with their lower leg, in particular riveted, to the free end of the arm of the U-shaped profile in such a way that the legs point outward in the same direction as the free arms, in which condition the arch and the upper leg of the U are freely pivotable, an elastically prestressed rocker for a parallelogram-like gear, whose counterpart rocker forms the leaf spring secured to the lower arm and for which the saw blade is the coupler, is created especially economically.
Because the lower leaf spring can be coupled to the motor, in particular by positive engagement, via drive means and in particular via a connecting rod, the transmission of the driving force does not take place directly to the saw blade, so that the reversal of motion at the dead center points along the path of motion of the saw blade is damped.
Because the lower leaf spring on its free end has a stamped, downward-curved tab that forms an eyelet for engagement by the connecting rod, an especially economical coupling between the connecting rod and the leaf spring is possible.
Because each leaf spring on each of its free ends has a respective groove extending transversely to the slot, in which groove one nipple of the saw blade can be centered and pivotably braced in articulated fashion, in particular with a knife-edge, the power fret saw blade can be coupled to the swinging leaf springs in an articulated fashion, without warping, in the parallelogram-like gear.
Because the nipples comprise extruded-on plastic and have a square region pointing toward the saw blade that reaches without play through the slot, the fastening ends of the power fret saw blade can be positioned in a securely centered and damped way relative to the leaf springs.
Because the U-shaped bracket comprises metal, in particular tubing of circular or elliptical cross section, and because the base and end housings are of plastic, in particular half housing shells to be put together, it is possible to combine sturdiness, achieved by great stability of the abutments of the power fret saw blade, with a lightweight construction and an ergonomic design of the power fret saw.